There is a trick that is actually a much faster way to load. This is how I do it in competition. I have some of the old 8 rounders, that I can actually force 9 into, and believe me, those ain't going in on a closed bolt.
I shoot with my left hand holding the magazine as a vertical foregrip.
On the last shot, I reach up with my right hand, (left still holding the mag, gun still on shoulder) and pull back the charging handle. I hold it back with my trigger finger, with my thumb grasping the receiver.
Now with my right hand holding the gun still against my shoulder, I drop the magazine with my left, and grab another mag with my left (from my vest). I rock and lock the mag into place, with the left hand automatically going into position (using the mag as vertical foregrip).
Then I just let go of the charging handle (chambering another round) and move my right hand back into firing position.
I can do this under 2 seconds on the clock, in a match, even while on the move.